Filament for incandescent electric lamps



citizen of the United States," I of East Orange in the county of Essexand State ofNew j tural changes resulting from the electric currentthrough the filaments.

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UNITED; stares "PATENT RALPH E. MYERS AND ROY D. HALL. EAST ORANGE, NEWJERSEY, .AS S IGNORS TO WESTINGHOUSE ILA MP COMPANY, A CORPORATION OFPENNSYLVANIA FILAMENT roa INCANDESGENT ELECTRIC LAMPS.

No Drawing."

ToaZZ'zchbmit inag I Be it known'thatwe, RALPH E. MYERS, a

and a resident ersey, and Roy D. HALL, a citizen of the United States,and a resident of East Orange in the county of Essex and State of Newjersey, have invented a new and useful Im rovement in Filaments forIncandescent Jlectric Lamps, of which the following is a specification.

ur invention relates to the manufacture of filamentary material, and ithas special reference to such filaments as constitute in: candescentbodies for electric lamps.

The ob ect of ourinvention is to provide filaments of theabove-indicated character which shall and which sistant to possess goodelectrical properties mechanical shocks and to strucg passage of 'Moreparticularly, the object of our invention is to provide metallicfilaments, composed largely or; mainly of metals of the tungsten type,which shall be highly resistant to the structural alterations known as loffsetting or faulting that tend to develop in this class of filamentsduring their use. r v .r

Certain materials. which are'suitable for use as filaments forincandescent-electric lamps have considerable mechanical strength whenfirst formed into filaments but become exceedingly fra ile er they havebeen traver'sed 'by electric c i fents. 'This phenomenon is acharacteristic oftufigsten filaments,

.whether such filaments are, prepared by squirting'or drawing processes,and it is have considerable initial strength and which,

' in the'case'of drawn tungsten wire, may even havea tensile, strengthmany times exceed- .they are found to have undergone marke structuralalterations, .The outline of such a filament shows lateral displacementof sections of the filament relativejto. one another,

and this displaced condition, which is known in the art asoffsetting,.or faulting, ap-

' pears to be caused by the development and,

Spectfieation of Letters Patent.

Application filed May 14,

shall. likewise be' durable and refound that pure tungsten filamentswhich ITIOZ.

Patented Dec. 21, 1920, 1915. Serial No: 28,163. w

growth of crystals within the body of the filament Such crystals seem toincrease in size in"much the same manner as crystals formed -in liquidsolutions, and, if the crystals become large enough to extend almost orentirely'across the filament, adjacent crystals tend to slip along theircleavage planes, thereby giving the'filament the ofi set of faultedappearance above referred to.

It therefore appears that internal crystal- .lization producesoffsetting and that ofisetting imparts brittleness. to the filaments.

The phenomenon described above becomes .-a particularly serious problem.in the manufacture of slender metallic filaments which are used in thesmaller types of incadescent o i-"i'cs.

lamps such as'25-watt, LO-wattand similar 7 lamps.

An eflicient method of resisting offsetting in lam filaments wasproposed, b Dr. A nton ederer and describel. in nited States Patent,#1,180,264 an the Westinghouse Lamp Company.

According. to Dr. Lederers method, and according to the.technicalpractice heretofore Tprevailing, the preferred additionmaterials are the oxids of the rear earth metals, particularlythorium'oxid. a We have discovered that the oifsetting'of lamp'filaments may be effectively prevented by the addition of small amountsof other assigned to refractory substances'which neither volatiliz nordecompose under the conditions existingsin glowing incandescentfilaments.

The u tances whlch' we have discovered to be particularly suitable forthis purpose are the oxids of the alkali metals, the alkaline earths,and also certainoxids belonging to such as berylllum I neither of theseclasses, oxid, aluminum oxid and, titanium oxid,

For the present purpose, we include magnesium ogzid' amo'ngthe alkaline:earths, as well as. calcium oxid, barium o'xid and strontium oxid. Ofthe alkali metal oxids,

we have found lithium oxid to be particu larly effective, and, of thealkaline earth .above, or mixtures of one or more of these substanceswith one"or more o'xids of rare earth metals, 1nclud1 ng thorium, oxid.Very '100 ogzids, calcium oxid and magnesium oxid are found also thatexcellent results reason why such improved results, are obtained withmixtures is not clear.

()ur invention 1s of special importance 1n the manufacture of tungstenfilaments, but

itmay also be applied to filaments composed of other metals, such asmolybdenum, tantalu'mand the like.

Very small amounts of ofiset resisting materials are sufficient togreatly retard the development of offsetting. A few hundredths of'oneper cent. are sometimes sut'-= ficient, and it is usually unnecessary toadd to the filaments more than 5% of their Weight of theoffset-resisting additions in order to obtain the maximum offset-resist--making drawn tungsten filaments, We ordinarily find it convenient toadd the offsetresisting materials to the powdered oxid before it isreduced to metal. The precise steps of the process of forming filamentsby 'drawing, squirting or otherwise form no part of ourpresentinvention. It is also to be understood that other limitationsarenot to be imposed thereon except as indicated in the ap ended claims.

k Ve claim as our invention: 1. A filament comprising drawn tungstenwire that tends to offset When utilized as a conductor of electricityand also containing calcium oxid and magnesium oxid.

2. A filament comprising tungsten that tends to offsetwhen utilized as aconductor of electricity and also containing at least two'of a group ofsubstances including the alkali metal ()XldS, the alkaline earths,

beryllium (mid aluminum oxid, and tilanrum dloxid.

In testimony whereof We have hereunto subscribed our name this th day ofApril,

RALPH E. MYERS. ROY D. HALL.

Witnesses ALFRED H. EDGERLEY, FREDERICK A. BET'rs.

